Glass substrate, liquid crystal antenna and high-frequency device

ABSTRACT

Provided is a glass substrate with which it is possible to reduce dielectric loss in high-frequency signals, and which also has excellent thermal shock resistance. This invention satisfies the relation {Young&#39;s modulus (GPa)×average thermal expansion coefficient (ppm/° C.) at 50-350° C.}≤300 (GPa·ppm/° C.), wherein the relative dielectric constant at 20° C. and 35 GHz does not exceed 10, and the dielectric dissipation factor at 20° C. and 35 GHz does not exceed 0.006.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior U.S. applicationSer. No. 17/550,080, filed Dec. 14, 2021, the disclosure of which isincluded herein by reference in its entirety. U.S. application Ser. No.17/550,080 is a continuation application of prior U.S. application Ser.No. 17/022,365, filed Sep. 16, 2020, issued as U.S. Pat. No. 11,239,549on Feb. 1, 2022, the disclosure of which is included herein by referencein its entirety. U.S. application Ser. No. 17/022,365 is a continuationof PCT/JP2019/010424, filed Mar. 13, 2019, the disclosure of which isincluded herein by reference in its entirety. U.S. application Ser. No.17/022,365 claims priority to Japanese Application No. 2018-053082,filed Mar. 20, 2018, the disclosure of which is included herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to a glass substrate, and to aliquid-crystal antenna and a high-frequency device each including theglass substrate.

BACKGROUND ART

In communication appliances such as mobile telephones, smartphones,personal digital assistants, and Wi-Fi appliances and other electronicdevices including surface acoustic wave (SAW) devices, radar components,and antenna components, the signal frequencies are being shifted tohigher frequencies in order to attain an increase in communicationcapacity, an increase in communication speed, etc. In general, thecircuit boards to be used in communication appliances and electronicdevices for such high-frequency applications employ insulatingsubstrates such as resin substrates, ceramic substrates, and glasssubstrates. Such insulating substrates for use in communicationappliances and electronic devices for high-frequency applications arerequired to be reduced in transmission loss due to dielectric loss,conductor loss, etc., in order to ensure the quality and properties suchas strength, of high-frequency signals.

For example, Patent Document 1 discloses that cross-talk noise can bediminished while maintaining a transmission loss at a conventionallevel, by employing an insulating substrate having a dielectric losstangent within a specific range and by forming a wiring layer having awiring width and a surface roughness which are within specific ranges.Patent Document 2 discloses that an electronic-circuit substrate reducedin relative permittivity or dielectric loss is obtained by using alead-free glass having a specific composition.

Among such insulating substrates, resin substrates intrinsically havelow rigidity. Because of this, it is difficult to use resin substratesfor semiconductor package products which are required to have rigidity(strength). Ceramic substrates have a drawback in that it is difficultto heighten the surface smoothness thereof and therefore conductor lossarising from the conductor formed on the substrate surface are easy tobe increased.

Meanwhile, glass substrates have high rigidity and hence facilitate sizeor thickness reduction or the like in packages, and also have excellentsurface smoothness. Glass substrates further have feature that it iseasy to be produced in larger size as substrates.

As a result of the spread of IoT, various devices have come to have acommunicating function and there comes to be the need of mountingcommunication devices even on products such as motor vehicles, in whichradio communication has not been performed so far. It has hence beenproposed to mount a communication device such as a liquid-crystalantenna on the roof of a motor vehicle to communicate with satellites(see Patent Documents 3 and 4).

CITATION LIST Patent Literature

Patent Document 1: JP-A-2013-077769

Patent Document 2: JP-A-2004-244271

Patent Document 3: JP-T-2017-506467 (The term “JP-T” as used hereinmeans a published Japanese translation of a PCT patent application.)

Patent Document 4: JP-T-2017-506471

SUMMARY OF INVENTION Technical Problem

However, the conventional glass substrates have large values ofdielectric loss tangent especially in the GHz band and it is difficulttherewith to maintain quality, strength, and other properties ofhigh-frequency signals. Furthermore, in cases when conventional glasssubstrates are to be perforated and used as perforated substrates, theglass substrates are prone to be cracked by thermal shocks caused bytemperature differences therein during laser processing for theperforation.

Meanwhile, in contrast to antennas intended to be used outdoors,communication devices have hitherto been used mainly indoors or inprotected spaces. However, in cases when liquid-crystal antennas and thelike are attached to motor vehicles, ships, and the like, theseappliances are used in severe environments involving considerabletemperature fluctuations. Because of this, the liquid-crystal antennasand the like, which are in the state of being exposed to the outsideair, are thought to be exposed to abrupt temperature changes, forexample, when the liquid-crystal antennas and the like in the state ofbeing hot in sunshine are suddenly cooled by rain. In such applications,the conventional glass substrates used in electronic devices are proneto be cracked by thermal shocks due to abrupt temperature changes.

Under these circumstances, an object of the present invention is toprovide: a glass substrate which can reduce the dielectric loss ofhigh-frequency signals and has excellent thermal-shock resistance; and aliquid-crystal antenna and a high-frequency device each employing theglass substrate.

Solution to the Problem

The present inventors diligently made investigations in order toovercome the problems and, as a result, have discovered that a glasssubstrate can be made to have excellent resistance to thermal shockscaused by abrupt temperature changes, by regulating the product of theYoung's modulus and the average coefficient of thermal expansion at50-350° C. to a value not larger than a given value. This glasssubstrate is hence suitable, for example, for use as a substrate forliquid-crystal antennas and the like, which are used in environmentsinvolving considerable temperature fluctuations, or as a substrate forhigh-frequency circuits which is subjected to perforation with a laser,etc.

The glass substrate of the present invention satisfies the followingrelationship:

{[Young's modulus (GPa)]×[average coefficient of thermal expansion at50-350° C. (ppm/° C.)]}≤300 (GPa·ppm/° C.), and

-   -   has a relative permittivity as measured at 20° C. and 35 GHz of        10 or less and a dielectric loss tangent as measured at 20° C.        and 35 GHz of 0.006 or less.

In one aspect of the glass substrate of the present invention, the glasssubstrate is for use in a liquid-crystal antenna or a high-frequencycircuit.

The present invention further provides, in one aspect thereof, aliquid-crystal antenna or a high-frequency device each including theglass substrate.

Advantageous Effects of the Invention

The glass substrate of the present invention can reduce the dielectricloss of high-frequency signals. This glass substrate further hasexcellent thermal-shock resistance and is hence suitable, for example,as a substrate to be used in an environment where the temperaturefluctuates considerably or as a substrate to be perforated with a laser,etc. This glass substrate hence makes it possible to provide aliquid-crystal antenna and a high-frequency device which have highperformance and are practical.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a cross-sectional view showing one example of theconfiguration of a high-frequency circuit.

DESCRIPTION OF EMBODIMENTS

The present invention will be explained below in detail, but the presentinvention should not be limited to the following embodiments and can bemodified at will within the gist of the present invention. Furthermore,the symbol “-” indicating a numerical range is used as a denotation of arange including the numerical values before and after the symbol “-” asa lower limit value and an upper limit value.

The contents of components of the glass substrate are each given in molepercentage on an oxide basis unless otherwise indicated. The term “highfrequency” means a frequency of 10 GHz or higher, and is preferablyhigher than 30 GHz, more preferably 35 GHz or higher.

<Glass Substrate>

The glass substrate (hereinafter often referred to simply as“substrate”) of the present invention is characterized by satisfying therelationship {[Young's modulus (GPa)]×[average coefficient of thermalexpansion at 50-350° C. (ppm/° C.)]}≤300 (GPa·ppm/° C.){[Young's modulus(GPa)]×[average coefficient of thermal expansion at 50-350° C. (ppm/°C.)]}≤300 (GPa·ppm/° C.) and having a relative permittivity as measuredat 20° C. and 35 GHz of 10 or less and a dielectric loss tangent asmeasured at 20° C. and 35 GHz of 0.006 or less.

Since the value represented by {[Young's modulus (GPa)]×[averagecoefficient of thermal expansion at 50-350° C. (ppm/° C.)]} (hereinafteroften referred to as “Expression 2”) is 300 GPa·ppm/° C. or less, thesubstrate receives reduced stress even when strained by a difference inthermal expansion and hence has improved thermal-shock resistance.

The value represented by Expression 2 is preferably 280 GPa·ppm/° C. orless, more preferably 250 GPa·ppm/° C. or less, still more preferably220 GPa·ppm/° C. or less, yet still more preferably 200 GPa·ppm/° C. orless. Meanwhile, there is no particular lower limit thereon, but thevalue represented by Expression 2 is preferably 100 GPa·ppm/° C. orhigher from the standpoints of ensuring the rigidity of the substrateand obtaining the substrate easy to be produced.

As the Young's modulus decreases, the value represented by Expression 2becomes smaller and the stress imposed on the substrate becomes lower,resulting in increase in thermal-shock resistance. Because of this, theYoung's modulus of the glass substrate is preferably 70 GPa or less,more preferably 67 GPa or less, still more preferably 64 GPa or less,yet still more preferably 60 GPa or less.

Meanwhile, in the case where the glass substrate is for use inhigh-frequency circuits, the glass substrate has a Young's modulus ofpreferably 40 GPa or higher, more preferably 50 GPa or higher, stillmore preferably 55 GPa or higher, from the standpoint of inhibiting thesubstrate from being deflected in high-frequency device production steps(wafer process) and thereby inhibiting the occurrence of productionfailures, etc.

The Young's modulus can be regulated by changing the composition andheat history of the glass to be used as the substrate. The Young'smodulus can be measured by an ultrasonic pulse method in accordance withthe method specified in JIS Z 2280 (year 1993).

A strain due to a thermal shock occurs as a result of thermal expansionor contraction due to a temperature difference between two points withinthe glass. Even under the same temperature difference, a lowercoefficient of thermal expansion results in a smaller strain and hencein an increase in thermal-shock resistance. Because of this, it ispreferable that the average coefficient of thermal expansion at 50-350°C. is low. The average coefficient of thermal expansion at 50-350° C. ispreferably 5 ppm/° C. or less, more preferably 4 ppm/° C. or less, stillmore preferably 3.5 ppm/° C. or less, yet still more preferably 3.3ppm/° C. or less. Furthermore, by making the average coefficient ofthermal expansion low, differences in thermal expansion coefficientbetween this substrate and other members can be more suitably regulatedduring production of a device or the like employing the substrate.

There is no particular lower limit thereto, but the average coefficientof thermal expansion at 50-350° C. is preferably 1.0 ppm/° C. or higher,more preferably 2.0 ppm/° C. or higher, from the standpoint of obtainingthermal properties suitable for forming.

The coefficient of thermal expansion can be regulated by changing thecontents of, in particular, alkali metal oxides or alkaline-earth metaloxides among the components of the glass to be used as the substrate orby changing the heat history of the glass.

The average coefficient of thermal expansion at 50-350° C. can bedetermined with a differential thermodilatometer in accordance with themethod specified in JIS R3102 (year 1995).

By reducing the relative permittivity and dielectric loss tangent of theglass substrate, the dielectric loss in a high-frequency range can bereduced.

At 20° C. and 35 GHz, the glass substrate has a relative permittivity of10 or less and a dielectric loss tangent (tanδ) of 0.006 or less. Therelative permittivity is preferably 8 or less, more preferably 6 orless, still more preferably 5 or less, yet still more preferably 4.5 orless. The relative permittivity is usually 4.0 or higher although thereis no particular lower limit thereon. The dielectric loss tangent ispreferably 0.005 or less, more preferably 0.004 or less, still morepreferably 0.0035 or less, yet still more preferably 0.003 or less. Thedielectric loss tangent is usually 0.0005 or higher although there is noparticular lower limit thereon.

At 20° C. and 10 GHz, the glass substrate preferably has a relativepermittivity of 10 or less and a dielectric loss tangent (tanδ) of 0.006or less. The relative permittivity is more preferably 8 or less, stillmore preferably 6 or less, yet still more preferably 5 or less,especially preferably 4.5 or less. The relative permittivity is usually4.0 or more each, although there is no particular lower limit thereon.The dielectric loss tangent is more preferably 0.005 or less, still morepreferably 0.004 or less, yet still more preferably 0.0035 or less,especially preferably 0.003 or less. The dielectric loss tangent isusually 0.0005 or higher although there is no particular lower limitthereon.

It is preferable that the values of relative permittivity and dielectricloss tangent as measured at 20° C. and 35 GHz are made closerespectively to the values of relative permittivity and dielectric losstangent as measured at 20° C. and 10 GHz to reduce the frequencydependence (dielectric dispersion), thereby making frequencycharacteristics of dielectric characteristics less apt to change andcausing only a slight design change even when frequency for use isdifferent.

The relative permittivity and the dielectric loss tangent can beregulated by changing the composition of the glass to be used as thesubstrate.

The relative permittivity and the dielectric loss tangent can bemeasured in accordance with the method specified in JIS R1641 (year2007) using a cavity resonator and a vector network analyzer.

In a glass substrate, a crack due to a thermal shock is prone to occurfrom an end surface of the substrate. Because of this, the lower thesurface roughness of the end surfaces of the substrate, the lower thedegree of stress concentration and the higher the thermal-shockresistance. The end surfaces of the substrate have a surface roughness,in terms of arithmetic mean roughness Ra, of preferably 1.5 nm or less,more preferably 1.0 nm or less, still more preferably 0.8 nm or less,yet still more preferably 0.5 nm or less, especially preferably 0.3 nmor less. The end surfaces of the glass substrate are the surfacesparallel with the thickness direction of the substrate.

The term “arithmetic mean roughness Ra” means a value obtained inaccordance with JIS B0601 (year 2001).

Examples of methods for regulating the surface roughness of the endsurfaces to a value within that range include processing techniques suchas a polishing treatment and etching in which a chemical, e.g.,hydrofluoric acid, is used.

Examples of the polishing treatment include: mechanical polishing inwhich an abrasive material including cerium oxide, colloidal silica, orthe like as a main component and a polishing pad are used; chemicalmechanical polishing in which a polishing slurry including an abrasivematerial and an acidic or alkaline liquid as a dispersion medium and apolishing pad are used; and chemical polishing in which an acidic liquidor an alkaline liquid is used as an etchant. Any of these polishingtreatments is used in accordance with the surface roughness of the glasssheet to be used as the material of the glass substrate. For example,preliminary polishing and finish polishing may be used in combination.

Since the substrate is prone to suffer breaking, cracking, chipping, orthe like which occurs from the end surfaces, it is preferable that atleast a part of the end surfaces have been chamfered in order to improvethe strength of the substrate. It is more preferred to form anend-surface chamfer shape having an obtuse angle, because a furtherimprovement in strength is attained thereby. Examples of modes ofchamfering include C-chamfering, R-chamfering, and light-chamfering. Twoor more of these may be used in combination to form a chamfer of acomplicated shape. Preferred of those are C-chamfering and R-chamfering.

C-chamfering is a chamfering method in which a corner portion between amain surface and an end surface is cut off obliquely. The angle formedby the surface perpendicular to the main surface of the substrate andthe surface formed by cutting off the corner portion is preferably 120°or larger, more preferably 135° or larger, still more preferably 175° orlarger.

R-chamfering is a chamfering method which forms a chamfer shape that isround as compared with ones formed by C-chamfering.

The chamfer surface resulting from the chamfering preferably has anarithmetic mean roughness Ra of 0.2 μm or less. The “arithmetic meanroughness Ra” is a value measured by a method according to JISB0601:2001 under the conditions of an evaluation length of 8 mm, acut-off value λc of 0.8 mm, and a cut-off ratio λc/λs of 100. By thusregulating the surface roughness thereof, cracking generating from thechamfer surface become less apt to occur. Examples of methods forregulating the arithmetic mean roughness Ra of the chamfer surface to0.2 μm or less include a method in which the chamfer surface is polishedwith a diamond film of #1000-3000.

The main surface of the glass substrate is a surface on which wiringlayer is formed in using the substrate, for example, in high-frequencycircuits. The main surface preferably has a surface roughness of 1.5 nmor less in terms of arithmetic mean roughness Ra. This is because awiring layer which is suffering a skin effect can be reduced in the skinresistance even in a high-frequency range exceeding 30 GHz, therebyattaining a reduction in conductor loss. The arithmetic mean roughnessRa of the main surface of the substrate is more preferably 1.0 nm orless, still more preferably 0.5 nm or less.

Such surface roughness of the main surface can be attained by subjectingthe main surface to a polishing treatment or the like according to need.For the polishing treatment, the same method as the polishing treatmentfor the end surfaces can be employed.

The shape of the substrate is not particularly limited. However, it ispreferable that one of the main surfaces has an area of 100 cm² orlarger, from the standpoint of the transmission/reception efficiency ofantennas, etc. The area thereof is more preferably 225 cm² or larger.Meanwhile, the area thereof is preferably 100,000 cm² or less from thestandpoint of handleability of the substrate, and is more preferably10,000 cm² or less, still more preferably 3,600 cm² or less.

The thickness of the substrate is preferably 0.01 mm or larger from thestandpoint of maintaining the strength of the substrate, and is morepreferably 0.05 mm or larger. From the standpoint of enhancing theultraviolet-shielding ability to make it possible to protect resinswhich are deteriorated by ultraviolet light, the thickness of thesubstrate is still more preferably 0.1 mm or larger, yet still morepreferably larger than 0.2 mm.

Meanwhile, from the standpoints of attaining thickness reduction andsize reduction in high-frequency devices employing high-frequencycircuits or in liquid-crystal antennas, and the standpoints of attainingan improvement in the efficiency of production thereof, etc., thethickness of the substrate is preferably 2 mm or less, more preferably 1mm or less. Furthermore, the thickness thereof is still more preferably0.7 mm or less, yet still more preferably 0.5 mm or less, from thestandpoint of heightening the ultraviolet transmittance to make itpossible to use an ultraviolet-curable material in steps for producingdevices, antennas, etc., thereby heightening the production efficiency.

The Vickers hardness of the substrate is preferably 400 or higherbecause the substrate having such hardness is less apt to crack uponreception of a mechanical shock, and is more preferably 450 or higher,still more preferably 500 or higher. The Vickers hardness thereof ispreferably 550 or less.

The Vickers hardness can be regulated by changing the glass compositionin the substrate. The Vickers hardness can be measured by a methodaccording to JIS R1310 (2003).

The cracking load of the substrate is preferably higher than 1.96 N,more preferably 4.9 N or higher, still more preferably 9.8 N or higher,especially preferably higher than 19.6 N, because the substrate havingsuch cracking load is less apt to crack upon reception of a mechanicalshock.

The cracking load can be regulated by changing the glass composition orheat history in the substrate or by changing a surface processing to begiven to the substrate. The cracking load can be determined using aVickers hardness meter by measuring a load at which the rate of crackoccurrence exceeds 50%.

The density of the substrate is preferably 2.5 g/cm³ or less, morepreferably 2.4 g/cm³ or less, still more preferably 2.35 g/cm³ or less,yet still more preferably 2.3 g/cm³ or less, from the standpoints ofattaining a weight reduction in devices, antennas, or the like employingthe substrate and of reducing the brittleness of the glass to make thesubstrate less apt to crack against thermal shock or mechanical shock.The density thereof is usually 2.0 g/cm³ or higher, although there is noparticular lower limit thereon. The density can be measured byArchimedes method.

It is preferable that at least one main surface of the substrate has acompressive stress layer formed in at least a part thereof, from thestandpoint of making the substrate less apt to crack against thermalshock or mechanical shock. The compressive stress layer can be formed,for example, by a strengthening treatment, and either a physicalstrengthening treatment or a chemical strengthening treatment can beemployed. For both the physical strengthening treatment and the chemicalstrengthening treatment, conventionally known methods can be used.

The porosity of the substrate is preferably 0.1% or less, morepreferably 0.01% or less, still more preferably 0.001% or less, from thestandpoint that such porosity is effective in producing high-frequencydevices inhibited from suffering noises, etc. In the case ofliquid-crystal antennas, the porosity of the substrate is preferably0.0001% or less from the standpoint of inhibiting wiring failures due toexposure of open pores in the surface.

The porosity can be determined by examining the bubbles contained in theglass substrate with an optical microscope, determining the number anddiameters of the bubbles, and calculating the volume of bubblescontained per unit volume.

The substrate preferably has a transmittance for light having 350-nmwavelength of 50% or higher, because such transmittance makes itpossible to use an ultraviolet-curable material in laminating steps,etc. in producing high-frequency devices, antennas, etc., therebyheightening the production efficiency. The transmittance thereof is morepreferably 70% or higher from the standpoints of reducing the period ofirradiating the ultraviolet-curable material with ultraviolet light insteps for producing devices, antennas, etc. and reducing thethickness-direction unevenness in curing of the ultraviolet-curablematerial.

For the same reasons as shown above, the substrate has a transmittancefor light having 300-nm wavelength of preferably 50% or higher, morepreferably 60% or higher, still more preferably 70% or higher. Thesubstrate has a transmittance for light having 250-nm wavelength ofpreferably 5% or higher, more preferably 10% or higher, still morepreferably 20% or higher.

Meanwhile, in the case of employing members made of resins that aredeteriorated by ultraviolet light for producing devices, antennas, andthe like, the transmittance for light having 350-nm wavelength ispreferably 80% or less, more preferably 60% or less, still morepreferably 30% or less, most preferably 10% or less, from the standpointof imparting ultraviolet-shielding ability to the substrate to enablethe substrate to function as a protective material.

For the same reason as shown above, the substrate has a transmittancefor light having 300-nm wavelength of preferably 80% or less, morepreferably 60% or less, still more preferably 30% or less, yet stillmore preferably 10% or less. The transmittance for light having 250-nmwavelength is preferably 60% or less, more preferably 30% or less, stillmore preferably 10% or less, yet still more preferably 5% or less.

The light transmittances of the substrate for the respective wavelengthscan be measured with a visible-ultraviolet spectrophotometer, andexternal transmittances including a loss due to reflection are used.

The β-OH of a substrate is a value used as an index to the water contentof the glass, and is determined by examining the glass substrate for theabsorbance of light having a wavelength of 2.75-2.95 μm and dividing themaximum value β_(max) thereof by the thickness (mm) of the substrate.

Regulating the β-OH value thereof to 0.8 mm⁻¹ or less is preferredbecause this enables the substrate to have further improvedlow-dielectric-loss characteristics. The β-OH value thereof is morepreferably 0.6 mm⁻¹ or less, still more preferably 0.5 mm⁻¹ or less, yetstill more preferably 0.4 mm⁻¹ or less.

Meanwhile, regulating the β-OH value of the substrate to 0.05 mm⁻¹ orlarger is preferred because this is effective in heightening glassproduction efficiency and enhancing property of bubbles, etc. withoutnecessity of melting in an extreme dry atmosphere or highly reducing thewater content of raw materials. The β-OH value thereof is morepreferably 0.1 mm⁻¹ or larger, still more preferably 0.2 mm⁻¹ or larger.

The β-OH value can be regulated by changing the composition of the glassfor the substrate, selecting a heat source for melting, changing themelting time, or selecting raw materials.

The substrate preferably has a devitrification temperature of 1,400° C.or lower. In cases when the devitrification temperature thereof is1,400° C. or lower, the forming equipment can be made to have lowermember temperatures in forming the glass, making it possible to prolongthe lives of the members. The devitrification temperature thereof ismore preferably 1,350° C. or lower, still more preferably 1,330° C. orlower, especially preferably 1,300° C. or lower.

The devitrification temperature of a glass is determined by placingcrushed particles of the glass on platinum dishes, heat-treating theglass particles for 17 hours in electric furnaces each having acontrolled constant temperature, examining the heat-treated samples withan optical microscope to measure a maximum temperature at which crystalprecipitation has occurred in the surface of and inside the glass and aminimum temperature at which crystal precipitation has not occurred, andaveraging the maximum and minimum temperatures.

The glass constituting the substrate is a solid which is amorphous andshows a glass transition. Neither a crystallized glass which is amixture of a glass and a crystalline substance nor a sintered glasscontaining a crystalline filler is included. The crystallinity of aglass may be determined, for example, by X-ray diffractometry. In caseswhen no clear diffraction peak is observed in an examination by X-raydiffractometry, then this glass can be ascertained to be amorphous.

Although a process for producing the glass substrate will be describedlater in detail, the glass substrate is formed by melting glass rawmaterials and hardening the melt. Methods for producing the substrateare not particularly limited. However, use can be made of, for example,a method in which a general molten glass is formed by the float processinto a sheet having a given thickness, annealed, and then cut into adesired shape to obtain a sheet glass.

The composition of the glass constituting the substrate is explainedbelow. In this description, the expression “substantially not contained”means that the glass does not contain a component other than thecomponent mixed therein as unavoidable impurities from raw materials,etc. Namely, that expression means that the component is not purposelyincorporated, and the content thereof is about 0.1% by mole or less.However, the content thereof is not limited to such values.

It is preferable that the glass includes SiO₂ as a main component. Inthis description, the expression “as a main component” means that thecontent of SiO₂ is the highest among the contents of components in molepercentage on an oxide basis. SiO₂ is a network-forming substance. Thecontent thereof is more preferably 40% or higher, still more preferably45% or higher, yet still more preferably 50% or higher, especiallypreferably 55% or higher, because such SiO₂ contents are effective inimproving the glass-forming ability and weatherability and in inhibitingdevitrification. Meanwhile, from the standpoint of attainingsatisfactory glass meltability, the content thereof is preferably 75% orless, more preferably 74% or less, still more preferably 73% or less,yet still more preferably 72% or less.

The total content of Al₂O₃ and B₂O₃ (the content of Al₂O₃ may be 0) ispreferably 1% or higher, more preferably 3% or higher, still morepreferably 5% or higher, yet still more preferably 7% or higher, becausesuch total contents are effective in enhancing the meltability of theglass, etc. Meanwhile, the total content of Al₂O₃ and B₂O₃ is preferably40% or less, more preferably 37% or less, still more preferably 35% orless, yet still more preferably 33% or less, because such total contentsare effective in heightening the low-dielectric-loss characteristics ofthe substrate while maintaining the meltability of the glass, etc.

The content molar ratio represented by {Al₂O₃/(Al₂O₃+B₂O₃)} ispreferably 0.45 or less, more preferably 0.4 or less, still morepreferably 0.3 or less, because such content molar ratios are effectivein enhancing the low-dielectric-loss characteristics of the glasssubstrate. The content molar ratio represented by {Al₂O₃/(Al₂O₃+B₂O₃)}is preferably 0 or larger (including 0), more preferably 0.01 or larger,still more preferably 0.05 or larger.

The content of Al₂O₃ is preferably 15% or less, more preferably 14% orless, still more preferably 10% or less, because such Al₂O₃ contents areeffective in improving the meltability of the glass, etc. Although theglass may not contain Al₂O₃, the content of Al₂O₃, when it is contained,is more preferably 0.5% or higher, since Al₂O₃ is a component effectivein improving the weatherability, inhibiting the glass from separatinginto phases, reducing the coefficient of thermal expansion, etc.

The content of B₂O₃ is preferably 30% or less, more preferably 28% orless, still more preferably 26% or less, yet still more preferably 24%or less, especially preferably 23% or less, because such B₂O₃ contentsare effective in making the acid resistance and the strain pointsatisfactory. Meanwhile, since B₂O₃ is a component effective inimproving the melting reactivity, lowering the devitrificationtemperature, etc., the content thereof is preferably 9% or higher, morepreferably 13% or higher, still more preferably 16% or higher.

Examples of alkaline-earth metal oxides include MgO, CaO, SrO, and BaO.These alkaline-earth metal oxides each function as a component enhancingthe melting reactivity of the glass. The total content of suchalkaline-earth metal oxides is preferably 13% or less, more preferably11% or less, still more preferably 0% or less, yet still more preferably8% or less, especially preferably 6% or less, because such totalcontents are effective in enhancing the low-dielectric-losscharacteristics of the glass substrate. Meanwhile, from the standpointof keeping the meltability of the glass satisfactory, the total contentof alkaline-earth metal oxides is preferably 0.1% or higher, morepreferably 3% or higher, still more preferably 5% or higher.

Although MgO is not essential, it is a component which can heighten theYoung's modulus without increasing the specific gravity. That is, MgO isa component capable of heightening the specific modulus. Byincorporating MgO, the problem of deflection can be alleviated and thefracture toughness value can be improved to enhance the glass strength.MgO is also a component which improves the meltability. Although MgO isnot an essential component, the content thereof is preferably 0.1% orhigher, more preferably 1% or higher, still more preferably 3% orhigher, because such MgO contents can sufficiently provide the effectsof MgO incorporation and are effective in inhibiting the coefficient ofthermal expansion from becoming too low. Meanwhile, from the standpointof inhibiting the devitrification temperature from rising, the contentof MgO is preferably 13% or less, more preferably 11% or less, stillmore preferably 9% or less.

CaO has a characteristics of heightening the specific modulus secondbehind MgO among the alkaline-earth metal oxides, and of not excessivelylowering the strain point. CaO is a component improving the meltabilitylike MgO. CaO is also a component characterized by being less prone toheighten the devitrification temperature as compared with MgO. AlthoughCaO is not an essential component, the content thereof is preferably0.1% or higher, more preferably 1% or higher, still more preferably 3%or higher, because such CaO contents can sufficiently provide theeffects of CaO incorporation. Meanwhile, from the standpoints ofpreventing the average coefficient of thermal expansion from becomingtoo high and of inhibiting the devitrification temperature from risingto prevent the glass from devitrifying when produced, the content of CaOis preferably 13% or less, more preferably 10% or less, still morepreferably 8% or less.

SrO is a component which improves the meltability of the glass withoutheightening the devitrification temperature thereof. Although SrO is notan essential component, the content thereof is preferably 0.1% orhigher, more preferably 0.5% or higher, still more preferably 1% orhigher, yet still more preferably 1.5% or higher, especially preferably2% or higher, because such SrO contents can sufficiently provide theeffect of SrO incorporation. Meanwhile, the content of SrO is preferably13% or less, more preferably 10% or less, still more preferably 7% orless, especially preferably 5% or less, because such SrO contents areeffective in inhibiting the average coefficient of thermal expansionfrom becoming too high without excessively increasing the specificgravity.

Although BaO is not essential, it is a component which improves themeltability of the glass without elevating the devitrificationtemperature thereof. However, the glass containing a large amount of BaOtends to have a large specific gravity, a reduced Young's modulus, aheightened relative permittivity, and too high average coefficient ofthermal expansion. Consequently, the content of BaO is preferably 10% orless, more preferably 8% or less, still more preferably 5% or less, yetstill more preferably 3% or less. It is especially preferable that BaOis substantially not contained.

The contents of the components of the glass which were shown above areused to determine a value represented by the Expression 1 below. It ispreferable that the value of the Expression 1 is 300 or less, sincestress generated in the substrate is reduced even when the substrate isstrained by a difference in thermal expansion and hence the substratehas improved thermal-shock resistance. The value represented byExpression 1 is more preferably 280 or less, still more preferably 250or less, yet still more preferably 220 or less, especially preferably200 or less. Although there is no particular lower limit thereon, thevalue represented by Expression 1 is preferably 100 or larger from thestandpoint of obtaining thermal properties suitable for forming.

(1.02×SiO₂+3.42×Al₂O₃+0.74×B₂O₃+9.17×MgO++12.55×CaO13.85×SrO+14.44×BaO+31.61×Na₂O+0.35×K₂O)  Expression 1

Examples of alkali metal oxides include Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O.The total content of such alkali metal oxides is preferably 5% or less,more preferably 3% or less, still more preferably 1% or less, yet stillmore preferably 0.2% or less, especially preferably 0.1% or less, mostpreferably 0.05% or less, from the standpoint of heightening thelow-dielectric-loss characteristics of the glass substrate. Meanwhile,the total content thereof is preferably 0.001% or higher, morepreferably 0.002% or higher, still more preferably 0.003% or higher, yetstill more preferably 0.005% or higher, because such total contents areeffective in obtaining practical glass meltability and glass substrateproduction efficiency without necessitating excessive raw-materialpurification and in regulating the coefficient of thermal expansion ofthe glass substrate.

Na₂O and K₂O are especially important among those alkali metal oxides,and it is preferable that the total content of Na₂O and K₂O is in therange of 0.001-5%.

The incorporation of Na₂O and K₂O in combination is preferred becausethis inhibits alkali components from moving and is hence able to enhancethe low-dielectric-loss characteristics of the glass substrate. That is,the content molar ratio represented by {Na₂O/(Na₂O+K₂O)} is preferably0.01-0.99, more preferably 0.98 or less, still more preferably 0.95 orless, yet still more preferably 0.9 or less. Meanwhile, the contentmolar ratio represented by {Na₂O/(Na₂O+K₂O)} is preferably 0.02 orlarger, more preferably 0.05 or larger, still more preferably 0.1 orlarger.

Besides containing the components described above, the glass maycontain, for example, Fe₂O₃, TiO₂, ZrO₂, ZnO, Ta₂O₅, WO₃, Y₂O₃, La₂O₃,etc. as optional components.

Among these, Fe₂O₃ is a component which controls the light-absorbingperformances, e.g., infrared-absorbing performance andultraviolet-absorbing performance, of the glass substrate. According toneed, Fe can be incorporated in an amount up to 0.012% in terms of Fe₂O₃amount. In cases when the content of Fe is 0.012% or less, thelow-dielectric-loss characteristics and ultraviolet transmittance of theglass substrate can be maintained. In the case where the glass containsFe, the content thereof is more preferably 0.01% or less, still morepreferably 0.005% or less, from the standpoint of improving theultraviolet transmittance. Heightening the ultraviolet transmittance ofthe glass substrate makes it possible to use an ultraviolet-curablematerial in laminating steps, etc. in producing high-frequency devices,antennas, etc., thereby heightening the efficiency of producing thehigh-frequency devices, antennas, etc.

Meanwhile, it is preferable that the glass substrate contains Fe in anamount of 0.05% or larger in terms of Fe₂O₃ amount according to need,because this can enhance the ultraviolet-shielding ability. The contentof Fe is more preferably 0.07% or higher, still more preferably 0.1% orhigher. By thus enhancing the ultraviolet-shielding ability of the glasssubstrate, the glass substrate can be made to function as a protectivematerial in cases when resins which are deteriorated by ultravioletlight are used as members.

<Process for Producing the Glass Substrate>

A process for producing the glass substrate includes: a melting step inwhich raw materials for glass are heated to obtain a molten glass; arefining step in which the molten glass is degassed; a forming step inwhich the molten glass is formed into a sheet shape to obtain a glassribbon; and an annealing step in which the glass ribbon is graduallycooled to a room-temperature state. The glass substrate may be producedalso by forming the molten glass into a block shape and subjecting theformed glass to annealing and then to cutting and polishing.

In the melting step, raw materials are prepared so as to result in adesired glass-substrate composition, continuously introduced into amelting furnace, and heated preferably at about 1,450° C.-1,750° C. toobtain a molten glass.

Usable as the raw materials are oxides, carbonates, nitrates,hydroxides, halides including chlorides, etc. In the case where themelting or refining step includes a step in which the molten glass comesinto contact with platinum, there are cases where minute platinumparticles are released into the molten glass and undesirably come ascontamination into the glass substrate to be obtained. The use ofraw-material nitrates has the effect of preventing the formation ofplatinum contamination.

Usable as the nitrates are strontium nitrate, barium nitrate, magnesiumnitrate, calcium nitrate, and the like. It is more preferred to usestrontium nitrate. With respect to raw-material particle sizes, use canbe suitably made of raw materials ranging from a particle diameter whichis large, e.g., several hundred micrometers, to such a degree that theparticles do not remain unmelted, to a particle diameter which is small,e.g., about several micrometers, to such a degree that the particlesneither fly off during raw-material conveyance nor aggregate to formsecondary particles. Particles formed by granulation are also usable.

The moisture contents of raw materials can be suitably regulated inorder to prevent the raw materials from flying off. Melting conditionsincluding β-OH value and the degree of Fe oxidation-reduction (redox[Fe²⁺+/(Fe²⁺+Fe³⁺)]) can be suitably regulated before the raw materialsare used.

The refining step is a step for degassing the molten glass obtained inthe melting step. In the fining step, use may be made of a method ofdegassing by depressurization or a method in which the molten glass isdegassed by heating to a temperature higher than the melting temperatureof the raw materials. In steps for producing glass substrates ofembodiments, SO₃ or SnO₂ can be used as a refining agent.

Preferred SO₃ sources are sulfates of at least one element selected fromthe group consisting of Al, Na, K, Mg, Ca, Sr, and Ba. More preferredare sulfates of alkaline-earth metals. Especially preferred of these areCaSO₄·2H₂O, SrSO₄, and BaSO₄, which are highly effective in enlargingthe bubbles.

In the method of degassing by depressurization, it is preferred to use ahalogen, such as Cl or F, as a refining agent.

Preferred Cl sources are chlorides of at least one element selected fromthe group consisting of Al, Mg, Ca, Sr, and Ba. More preferred arechlorides of alkaline-earth metals. Especially preferred of these areSrCl₂·6H₂O and BaCl₂·2H₂O, because these chlorides are highly effectivein enlarging the bubbles and have low deliquescence.

Preferred F sources are fluorides of at least one element selected fromthe group consisting of Al, Na, K, Mg, Ca, Sr, and Ba. More preferredare fluorides of alkaline-earth metals. Preferred of these is CaF₂ whichis highly effective in enhancing the meltability of the raw materialsfor glass.

Tin compounds represented by SnO₂ evolve O₂ gas in the glass melt. Inthe glass melt, SnO₂ is reduced to SnO at temperatures not lower than1,450° C. to evolve O₂ gas and thereby have the function of considerablyenlarging the bubbles. In producing glass substrates of embodiments, rawmaterials for glass are melted by heating to about 1,450-1,750° C. and,hence, the bubbles in the glass melt are more effectively enlarged.

In the case of using SnO₂ as a refining agent, the amount of tincompounds in the raw materials is regulated such that the contentthereof is 0.01% or higher in terms of SnO₂ amount with respect to thetotal amount of the base composition described above taken as 100%.Regulating the SnO₂ content to 0.01% or higher is preferred because therefining function is obtained in melting the raw materials for glass.The content of SnO₂ is more preferably 0.05% or higher, still morepreferably 0.10% or higher. Meanwhile, regulating the SnO₂ content to0.3% or less is preferred because the glass is inhibited from having acolor or devitrifying. The content of tin compounds in the alkali-freeglass is more preferably 0.25% or less, still more preferably 0.2% orless, especially preferably 0.15% or less, in terms of SnO₂ amount withrespect to the total amount of the base composition taken as 100%.

The forming step is a step in which the molten glass which has beendegassed in the refining step is formed into a sheet shape to obtain aglass ribbon. In the forming step, known methods for forming a glassinto a sheet shape can be used, such as a float process in which amolten glass is poured onto a molten metal, e.g., tin, and therebyformed into a sheet shape to obtain a glass ribbon, an overflow downdrawprocess (fusion process) in which a molten glass is caused to flowdownward from a trough-shaped member, and a slit downdraw process inwhich a molten glass is caused to flow downward through a slit.

The annealing step is a step in which the glass ribbon obtained in theforming step is cooled to a room-temperature state under controlledcooling conditions. In the annealing step, the glass ribbon is cooled sothat in the temperature range of from the annealing point to the strainpoint of the formed glass, the glass ribbon is cooled at a given averagecooling rate R (° C./min) and that the glass ribbon is further cooledgradually to a room-temperature state under given conditions. Theannealed glass ribbon is cut to obtain a glass substrate.

The given average cooling rate R [cooling rage (R)] is explained below.

In case where the cooling rate (R) in the annealing step is too high,the cooled glass is prone to have a residual strain therein. Inaddition, the too high cooling rate (R) results in an increase inequivalent cooling rate, which is a parameter reflecting fictivetemperature, making it impossible to obtain low-dielectric-losscharacteristics. It is hence preferred to set the R so as to result inan equivalent cooling rate of 800° C./min or less. The equivalentcooling rate is more preferably 400° C./min or less, still morepreferably 100° C./min or less, especially preferably 50° C./min orless. Meanwhile, in case where the cooling rate is too low, the steprequires too long a time period, resulting in a decrease in productionefficiency. It is hence preferred to set the R so as to result in anequivalent cooling rate of 0.1° C./min or higher. The equivalent coolingrate is more preferably 0.5° C./min or higher, still more preferably 1°C./min or higher.

A definition of the equivalent cooling rate and a method for evaluationthereof are as follows.

A glass having a composition to be examined, which has been processedinto rectangular parallelepipeds having dimensions of 10 mm×10mm×0.3-2.0 mm, is held at [strain point]+170° C. for 5 minutes using aninfrared heating type electric furnace and then cooled to roomtemperature (25° C.). In this operation, cooling rates ranging from 1°C./min to 1,000° C./min are used for the cooling to produce a pluralityof glass samples.

A precision refractometer (e.g., KPR2000, manufactured by ShimadzuDevice Corp.) is used to measure the refractive index n_(d) for d-line(wavelength, 587.6 nm) of each of the plurality of glass samples. Forthe measurement, a V-block method or a minimum deviation method may beused. The obtained values of n_(d) are plotted against the logarithm ofcooling rate, thereby obtaining a calibration curve showing arelationship between n_(d) and the cooling rate.

Next, the n_(d) of a glass having the same composition actually producedby the steps of melting, forming, cooling, etc. is measured by themeasuring method shown above. A corresponding cooling rate whichcorresponds to the measured value of n_(d) (in this embodiment, thecorresponding cooling rate is referred to as equivalent cooling rate) isdetermined from the calibration curve.

Although a process for producing the glass substrate was describedabove, production processes are not limited to the embodiment.Modifications, improvements, etc. within a range where the objects ofthe present invention can be attained are included in the presentinvention. For example, in producing a glass substrate of the presentinvention, a molten glass may be directly formed into a sheet shape bypress molding.

In the case of producing a glass substrate of the present invention,besides a production process in which a melting furnace made of arefractory material is used, the glass substrate may be produced by amethod in which a crucible made of platinum or an alloy includingplatinum as a main component (hereinafter referred to as platinumcrucible) is used as a melting furnace or a clarifier. In the case ofusing a platinum crucible in a melting step, raw materials are preparedso as to result in the composition of the glass substrate to be obtainedand the platinum crucible containing the raw materials is heated in anelectric furnace preferably to about 1,450° C.-1,700° C. A platinumstirrer is inserted thereinto to stir the contents for 1-3 hours toobtain a molten glass.

In a forming step in glass sheet production steps in which a platinumcrucible is used, the molten glass is poured, for example, on a carbonboard or into a mold and is thereby formed into a sheet or block shape.In an annealing step, the formed glass is held typically at atemperature higher than the glass transition point Tg by about 50° C.,thereafter cooled to around the strain point at a rate of about 1-10°C./min, and then cooled to a room-temperature state at a cooling ratewhich does not result in a residual strain. The glass sheet or block isthen cut into a given shape and polished, thereby obtaining a glasssubstrate. The glass substrate obtained by the cutting may be heated to,for example, a temperature of about Tg+50° C. and then gradually cooledto a room-temperature state at a given cooling rate. Thus, theequivalent cooling temperature of the glass can be regulated.

<High-Frequency Circuit, Liquid-Crystal Antenna>

The glass substrate of the present invention is suitable for use as asubstrate for circuit boards for high-frequency devices (electronicdevices) such as semiconductor devices for use in, for example,communication appliances such as mobile telephones, smartphones,personal digital assistants, and Wi-Fi appliances, surface acoustic wave(SAW) devices, radar components such as radar transceivers, etc. andsuitable for use as a substrate for components of antennas such asliquid-crystal antennas, etc. The substrate of the present invention ismore suitable for use as a substrate for high-frequency circuits to beused in high-frequency devices and for liquid-crystal antennas, becausethe substrate is especially effective in reducing the dielectric loss ofhigh-frequency signals and has excellent thermal-shock resistance.

In the case of the substrate for high-frequency circuits, the presentinvention is especially suitable for high-frequency devices in whichhigh-frequency signals, especially signals having a frequency higherthan 30 GHz, in particularly, 35 GHz or higher, are handled. Thus, thetransmission loss of such high-frequency signals can be reduced, makingit possible to improve the quality, strength, and other properties ofthe high-frequency signals.

The substrate of the present invention is suitable also for use as aperforated substrate produced using, for example, a laser. The substratenot only is effective in improving the quality, strength, and otherproperties of high-frequency signals as stated above but also has highresistance to thermal shocks during perforation.

An example (cross-sectional view) of the configuration of ahigh-frequency circuit for use in high-frequency devices is shown inFIG. 1 . The circuit board 1 includes a glass substrate 2 havinginsulating properties, a first wiring layer 3 formed on a first mainsurface 2 a of the glass substrate 2, and a second wiring layer 4 formedon a second main surface 2 b of the glass substrate 2. The first andsecond wiring layers 3 and 4 form microstrip lines as an example oftransmission lines. The first wiring layer 3 constitutes a signal line,and the second wiring layer 4 constitutes a ground line. However, thestructures of the first and second wiring layers 3 and 4 are not limitedto those, and a wiring layer may have been formed on only either of themain surfaces of the glass substrate 2.

The first and second wiring layers 3 and 4 are layers each constitutedof a conductor, and the thickness thereof is usually about 0.1-50 μm.

The conductors constituting the first and second wiring layers 3 and 4are not particularly limited, and use is made, for example, of a metalsuch as copper, gold, silver, aluminum, titanium, chromium, molybdenum,tungsten, platinum, or nickel, or an alloy or metal compound containingat least one of these metals.

The structures of the first and second wiring layers 3 and 4 are notlimited to single-layer structures, and the first and second wiringlayers 3 and 4 each may have a multilayer structure such as a laminatedstructure composed of a titanium layer and a copper layer. Methods forforming the first and second wiring layers 3 and 4 are not particularlylimited, and use can be made of any of various known formation methodssuch as a printing method using a conductor paste, dipping method,plating, vapor deposition, and sputtering.

By using the glass substrate of the present invention in high-frequencycircuits, the circuit boards can be reduced in transmission loss athigh-frequencies. Specifically, the transmission loss at a frequency of,for example, 35 GHz can be reduced to preferably 1 dB/cm or less, morepreferably 0.5 dB/cm or less. Consequently, the quality, strength, andother properties of high-frequency signals, in particular,high-frequency signals having a frequency exceeding 30 GHz, especially35 GHz or higher, are maintained. It is hence possible to provide glasssubstrates and circuit boards which are suitable for high-frequencydevices in which such high-frequency signals are handled. Thus, thecharacteristics and quality of high-frequency devices in whichhigh-frequency signals are handles can be improved.

Meanwhile, among substrates for high-frequency circuits, there aresubstrates called universal substrates or perforated substrates, etc.Such a substrate includes an insulating sheet of base material that hasthrough holes and copper-foil lands formed thereon in a regular pattern(e.g., lattice pattern) arrangement and that further has copper-foilwiring lines formed thereon by etching which connect several of thelands. A laser or the like is used for forming the through holes and forthe etching. Examples of the laser include an excimer laser, an infraredlaser, a CO₂ laser, and a UV laser.

In forming through holes or performing etching, the glass substrateundergoes a temperature difference therein to receive a thermal shock.However, since the glass substrate of the present invention has highthermal-shock resistance, this glass substrate does not crack even uponreception of the thermal shock and withstands the formation of throughholes and the etching.

A liquid-crystal antenna is an antenna for satellite communication whichcan be controlled with respect to the direction of radio waves to betransmitted or received, using the liquid-crystal technology.Liquid-crystal antennas are suitable for use mainly on vehicles such asships, airplanes, and motor vehicles. Since liquid-crystal antennas areexpected to be used mainly outdoors, the liquid-crystal antennas arerequired not only to have stable properties under a wide temperaturerange but also to have resistance to thermal shocks due to abrupttemperature changes such as, for example, temperature changes occurringin movements between on the ground and in the sky or occurring insqualls in scorching deserts.

Use of the glass substrate of the present invention in liquid-crystalantennas makes it possible to provide stable properties over a widetemperature range. Furthermore, since the glass substrate has resistanceto abrupt temperature changes, the liquid-crystal antennas can be usedwithout suffering cracking. Use of the glass substrate in thisapplication is hence preferred.

EXAMPLES

The present invention is explained below in detail by reference toExamples, but the invention is not limited thereto.

Examples 1 to 26

Glass substrates having the compositions shown in Tables 1 to 4 andhaving thicknesses of 0.5-10 mm and a shape of 50×50 mm were prepared.The glass substrates were produced by a melting method using a platinumcrucible. Raw materials including silica sand were mixed together so asto result in a glass amount of 1 kg, thereby preparing each batch.Thereto were added 0.1-1% of sulfate in terms of SO₃ amount, 0.16% of F,and 1% of Cl in mass percentage on an oxide basis, with respect to 100%of the raw materials for the desired composition. The raw materials wereplaced in the platinum crucible and melted by heating in an electricfurnace at a temperature of 1,650° C. for 3 hours to obtain a moltenglass.

In the melting, a platinum stirrer was inserted into the platinumcrucible to stir the melt for 1 hour, thereby homogenizing the glass.The molten glass was poured onto a carbon plate and formed into a sheetshape, and the sheet-shaped glass was placed in an electric furnacehaving a temperature of about Tg+50° C. and held therein for 1 hour. Theelectric furnace was thereafter cooled to a temperature of Tg-100° C. ata cooling rate of 1° C./min and then allowed to cool until the glasscooled to room temperature.

The glass was thereafter cut and polished to obtain a glass sheet. Theend surfaces were chamfered (C/R chamfering) with a chamfering device.Examples of the glass-sheet chamfering device include the devicedescribed in JP-A-2008-49449, which is a device for chamfering glasssheet end surfaces using a rotary grindstone. The rotary grindstone maybe either a resin-bonded grindstone or a metal-bonded grindstone.Examples of abrasive grains for use in such grindstones include any oneof diamond, cubic boron nitride (CBN), alumina (Al₂O₃), silicon carbide(SiC), pumice, garnet, and the like or a combination of two or morethereof.

In Tables 1 to 4, Total RO^(*1) means the total content ofalkaline-earth metal oxides (MgO+CaO+SrO+BaO), and Total R₂O^(*2) meansthe total content of alkali metal oxides (Na₂O+K₂O).

The glass substrates obtained were examined for Expression 1, Young'smodulus, average coefficient of thermal expansion at 50-350° C.,Expression 2, relative permittivity (20° C.) at 10 GHz and 35 GHz,dielectric loss tangent (20° C.) at 10 GHz and 35 GHz, Vickers hardness,cracking load, density, specific modulus, porosity, transmittance forlight having 350-nm wavelength (converted transmittance for thickness of0.3-0.4 mm), β-OH value, and devitrification temperature.

The Expression 1 is a value calculated from the contents of componentsin mole percentage on an oxide basis, using below calculation:

{1.02×SiO₂+3.42×Al₂O₃+0.74×B₂O₃+9.17×MgO+12.55×CaO+13.85×SrO+14.44×BaO+31.61×Na₂O+20.35×K₂O}.

The Expression 2 is a value represented by {[Young's modulus(GPa)]×[average coefficient of thermal expansion at 50-350° C. (ppm/°C.)]}.

The values of Expression 1 are shown in Tables 1 to 4, and the otherresults are shown in Tables 5 to 8. In the tables, each numeral given inparentheses is a value determined by calculation, and each blank or “-”indicates that no measurement was made.

The methods used for determining the properties are shown below.

(Young's Modulus)

In accordance with the method specified in JIS Z 2280, a glass having athickness of 0.5-10 mm was examined by an ultrasonic pulse method. Theunit is GPa.

(Average Coefficient of Thermal Expansion)

In accordance with the method specified in JIS R3102 (year 1995), adifferential thermodilatometer was used to conduct a measurement in thetemperature range of 50-350° C. The unit is ppm/° C.

(Relative Permittivity, Dielectric Loss Tangent)

In accordance with the method specified in JIS R1641 (year 2007), ameasurement was made with a cavity resonator and a vector networkanalyzer. The measuring frequencies were 35 GHz and 10 GHz, which wereair resonance frequencies for the cavity resonator.

(Vickers Hardness)

In accordance with the method specified in JIS R1610 (year 2003), theVickers hardness of a glass was measured under a load of 100 gf.

(Cracking Load)

In the air having a relative humidity of about 40%, a Vickers indenter(diamond indenter) having the shape of a square pyramid was pushed intoa glass surface for 30 seconds. A pushing load at which cracks occuroutward from all the four corners of the indentation in a proportion of50% is taken as the cracking load. The cracking load can be determinedwith a commercial Vickers hardness tester. The cracking load is anaverage for 10 or more indentations.

(Density)

A glass lump weighing about 20 g and containing no bubbles was examinedfor density by Archimedes method. The unit is g/cm³.

(Porosity)

The porosity of a glass substrate was determined by examining thebubbles contained therein with an optical microscope, determining thenumber and diameters of the bubbles, and calculating the volume ofbubbles contained per unit volume.

(Transmittance)

The transmittance of a mirror-polished glass having a given thicknesswas measured with a visible-ultraviolet spectrophotometer. The externaltransmittance including a loss due to reflection was measured as thetransmittance and was shown as a converted value corresponding to aglass thickness of 0.3-0.4 mm.

(β-OH Value)

β-OH values were determined by the method described in the embodimentshown above. The unit is mm⁻¹.

(Specific Modulus)

The specific modulus was determined by calculation from the measuredvalues of density and Young's modulus. The unit is GPa·cm³/g.

(Devitrification Temperature)

The devitrification temperature of a glass was determined by placingcrushed particles of the glass on platinum dishes, heat-treating theglass particles for 17 hours in electric furnaces each having acontrolled constant temperature, examining the heat-treated samples withan optical microscope to measure a maximum temperature at which crystalprecipitation had occurred inside the glass and a minimum temperature atwhich crystal precipitation had not occurred, and averaging the maximumand minimum temperatures.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Composition SiO₂ 68.069.5 71.0 62.0 71.1 66.1 100 [mol %] Al₂O₃ 4.0 5.5 4.0 8.0 1.1 11.3 0B₂O₃ 21.0 15.0 21.3 23.0 0.0 7.8 0 Al₂O₃ + B₂O₃ 25.0 20.5 25.3 31.0 1.119.1 0 MgO 0.0 3.0 0.0 4.0 6.9 5.1 0 CaO 1.0 4.0 0.0 2.0 8.3 4.5 0 SrO6.0 3.0 3.8 0.8 0.0 5.2 0 BaO 0.0 0.0 0.0 0.2 0.0 0.0 0 Total RO*¹ 7.010.0 3.8 7.0 15.2 14.8 0 Na₂O 0.009 0.007 0.012 0.01 12.4 0.07 0 K₂O0.003 0.004 0.006 0.005 0.2 0.01 0 Total R₂O*² 0.012 0.011 0.018 0.01512.6 0.08 0 Fe₂O₃ 0.002 0.001 0.003 0.01 0.04 0.003 0 RatioAl₂O₃/(Al₂O₃ + B₂O₃) 0.16 0.27 0.16 0.26 1 0.59 — Na₂O/(Na₂O + K₂O) 0.750.64 0.67 0.67 0.98 0.88 — Expression 1 195 220 155 184 640 290 102

TABLE 2 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Composition SiO₂ 62.060.0 60.0 58.0 62.0 58.0 [mol %] Al₂O₃ 10.0 10.0 10.0 10.0 8.0 10.0 B₂O₃21.0 23.0 26.0 26.0 23.0 25.0 Al₂O₃ + B₂O₃ 31.0 33.0 36.0 36.0 31.0 0.0MgO 2.0 2.0 1.0 3.0 2.0 2.0 CaO 3.0 3.0 2.0 2.0 3.0 3.0 SrO 2.0 2.0 1.01.0 2.0 2.0 BaO 0.0 0.0 0.0 0.0 0.0 0.0 Total RO*¹ 7.0 7.0 4.0 6.0 7.07.0 Na₂O 0.010 0.015 0.008 0.003 0.005 0.005 K₂O 0.003 0.003 0.005 0.0010.001 0.001 Total R₂O*² 0.013 0.018 0.013 0.004 0.006 0.006 Fe₂O₃ 0.0080.007 0.006 0.007 0.008 0.009 Ratio Al2O₃/(Al₂O₃ + B₂O₃) 0.32 0.30 0.280.28 0.26 0.29 Na₂O/(Na₂O + K₂O) 0.77 0.83 0.62 0.75 0.83 0.83Expression 1 197 197 163 179 191 196

TABLE 3 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Composition SiO₂ 60.060.0 60.0 60.0 60.0 60.0 [mol %] Al₂O₃ 8.0 10.0 5.0 2.0 0.0 0.0 B₂O₃25.0 23.0 28.0 31.0 33.0 36.0 Al₂O₃ + B₂O₃ 33.0 33.0 33.0 33.0 33.0 36.0MgO 2.0 4.0 2.0 2.0 2.0 1.0 CaO 3.0 2.0 3.0 3.0 3.0 2.0 SrO 2.0 1.0 2.02.0 2.0 1.0 BaO 0.0 0.0 0.0 0.0 0.0 0.0 Total RO*¹ 7.0 7.0 7.0 7.0 7.04.0 Na₂O 0.005 0.005 0.005 0.005 0.005 0.005 K₂O 0.001 0.001 0.001 0.0010.001 0.001 Total R₂O*² 0.006 0.006 0.006 0.006 0.006 0.006 Fe₂O₃ 0.0080.010 0.006 0.006 0.005 0.005 Ratio Al₂O₃/(Al₂O₃ + B₂O₃) 0.24 0.30 0.150.06 0.00 0.00 Na₂O/(Na₂O + K₂O) 0.83 0.83 0.83 0.83 0.83 0.83Expression 1 191 188 183 175 169 136

TABLE 4 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26 CompositionSiO₂ 60.0 63.0 62.0 64.0 65.0 62.0 64.0 [mol %] Al₂O₃ 10.0 8.0 8.0 9.010.0 7.2 8.5 B₂O₃ 21.0 16.0 23.0 18.5 14.0 23.0 18.5 Al₂O₃ + B₂O₃ 31.024.0 31.0 27.5 24.0 30.2 27.0 MgO 2.0 4.0 4.0 2.5 4.0 4.3 2.5 CaO 3.05.0 2.0 3.5 5.0 2.5 4.0 SrO 4.0 3.0 1.0 2.5 2.0 1.0 2.5 BaO 0.0 1.0 0.00.0 0.0 0.0 0.0 Total RO*¹ 9.0 13.0 7.0 8.5 11.0 7.8 9.0 Na₂O 0.01 0.0120.004 0.006 0.005 0.005 0.008 K₂O 0.002 0.003 0.001 0.001 0.001 0.0010.002 Total R₂O*² 0.012 0.015 0.005 0.007 0.006 0.006 0.010 Fe₂O₃ 0.0080.010 0.010 0.003 0.002 0.005 0.005 Ratio Al₂O₃/(Al₂O₃ + B₂O₃) 0.32 0.330.26 0.33 0.42 0.24 0.31 Na₂O/(Na₂O + K₂O) 0.83 0.80 0.80 0.86 0.83 0.830.80 Expression 1 223 259 183 211 238 190 216

TABLE 5 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Young's modulus 58 66(51)    59 73 76 74 [GPa] Average coefficient of 3.4 3.3 (2.8)  3.2 8.53.8 0.7 thermal expansion [ppm/° C.] Expression 2 197 218 (143)    189621 289 52 Relative permittivity 4.47 4.62 3.96 4.36 (6.80) 5.49 3.75 @10 GHz Relative permittivity 4.39 4.57 4.09 4.35 7.13 5.41 3.87 @ 35 GHzDielectric loss tangent 1.79 2.42 1.22 1.80 (22.0) 6.20 0.11 @ 10 GHz(×10⁻³) Dielectric loss tangent 2.48 3.04 1.82 2.61 20.9 8.98 0.15 @ 35GHz (×10⁻³) Vickers hardness 530 570 Cracking load [N] Higher than9.8-19.6N 19.6N Density [g/cm³] 2.32 2.34 (2.24) 2.26 2.49 2.50 2.20Specific modulus 25 28 23    26 29 30 34 [GPa · cm³/g] Porosity [%] 0 00   0 0 0 0 Transmittance [%] 90 90 90    90 90 90 93 (0.3-0.4 mmt) β-OH[mm-¹] 0.21 0.34 — 0.48 0.19 0.28 — Devitrification 1200° C. 1200° C.1200° C. 1220 1000° C. 1270 — temperature [° C.] or less or less or lessor less

TABLE 6 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Young's modulus [GPa]62    61    58    59    58 59    Average coefficient of thermal (3.0) (3.1)  (2.7)  (2.9)  3.3 (3.1)  expansion [ppm/° C.] Expression 2(190)    (189)    (158)    (171)    193 (186)    Relative permittivity4.56 4.56 4.34 4.42 4.41 4.53 @ 10 GHz Relative permittivity 4.59 4.584.39 4.43 4.43 4.55 @ 35 GHz Dielectric loss tangent 2.20 2.16 1.59 1.881.86 1.99 @ 10 GHz (×10⁻³) Dielectric loss tangent 3.27 3.25 2.32 2.742.86 3.38 @ 35 GHz (×10⁻³) Density [g/cm³] 2.30 2.30 2.25 2.26 2.27 2.29Specific modulus [GPa · cm³/g] 27    27    26    26    26 26    Porosity[%] 0   0   0   0   0 0   Transmittance [%] 90    90    90    90    9090    (0.3-0.4 mmt) β-OH [mm⁻¹] (0.35) (0.35) (0.35) (0.35) 0.43 (0.35)Devitrification temperature 1330     1295     1420° C. 1420° C. 11701310     [° C.] or more or more

TABLE 7 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Young's modulus [GPa]57    61    53    (42)    (39)    (35)    Average coefficient of thermal(3.1)  (2.9)  (3.2)  (3.3)  (3.4)  (3.0)  expansion [ppm/° C.]Expression 2 (180)    (179)    (172)    (140)    (130)    (104)   Relative permittivity 4.44 4.48 4.27 4.04 3.86 3.77 @ 10 GHz Relativepermittivity 4.46 4.51 4.26 4.10 3.84 3.79 @ 35 GHz Dielectric losstangent 1.81 1.99 1.55 1.29 1.60 1.74 @ 10 GHz (×10⁻³) Dielectric losstangent 2.76 2.98 2.39 1.94 1.85 2.01 @ 35 GHz (×10⁻³) Density [g/cm³]2.27 2.28 2.23 (2.20) (2.17) (2.11) Specific modulus [GPa-cm³/g] 25   27    24    19    18    16    Porosity [%] 0   0   0   0   0   0  Transmittance [%] 90    90    90    — — — (0.3-0.4 mmt) β-OH [mm¹] 0.48(0.35) 0.52 (0.35) (0.35) (0.35) Devitrification temperature 1160    1340     1040     — — — [° C.]

TABLE 8 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Ex. 25 Ex. 26 Young's modulus[GPa] (59)    (64)    (59) (64) (70)    59 64 Average coefficient of(3.4)  (3.8)  3.1 3.4 (3.4)  3.5 3.5 thermal expansion [ppm/° C.]Expression 2 (200)    (241)    (184) (214) (238)    208 223 Relativepermittivity (4.83) (5.12) 4.38 4.66 4.89 4.36 4.63 @ 10 GHz Relativepermittivity (4.85) (5.12) 4.34 4.63 4.84 4.36 4.61 @ 35 GHz Dielectricloss tangent (2.97) (4.01) 1.79 2.45 3.18 1.74 2.36 @ 10 GHz (×10⁻³)Dielectric loss tangent (4.23) (5.44) 2.64 3.40 4.80 2.63 3.56 @35 GHz(×10⁻³) Density [g/cm³] (2.36) (2.42) (2.26) (2.33) (2.38) (2.26) (2.33)Specific modulus 25    26    26 27 29    26 27 [GPa.cm³/g] Porosity [%]0   0   0 0 0   0 0 Transmittance [%] 90    90    90 90 90    90 90(0.3-0.4 mmt) β-OH [mm⁻¹] (0.35) (0.35) (0.35) (0.35) (0.35) 0.49 0.53Devitrification — — 1230 1220 1300 1290 1350 temperature [° C.]

As Tables 5 to 8 show, the product (value represented by Expression 2)of the coefficient of thermal expansion and the Young's modulus in eachof the glass substrates of the present invention is as small as 300 orless. These glass substrates are hence less apt to suffer tensile stresseven when undergoing an abrupt temperature difference. As a result, theglass substrates can be inhibited from being damaged by use environmentsinvolving an abrupt temperature change or by processing steps which areapt to cause a temperature difference.

Furthermore, since the glass substrates of the present invention eachhave a relative permittivity at 20° C. and 35 GHz of 10 or less and adielectric loss tangent at 20° C. and 35 GHz of 0.006 or less, the glasssubstrates can attain a reduction in dielectric loss in a high-frequencyrange.

Moreover, the glass substrates of the present invention can be processedunder small load because of their low Vickers hardnesses and are lessapt to have defects such as microcracks because of their high crackingloads, and consequently the glass substrates of the present inventionare obtained as high-strength substrates.

While the invention has been described in detail and with reference tospecific embodiments thereof, it is apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. This application is basedon a Japanese patent application filed on Mar. 20, 2018 (Application No.2018-53082), the entire contents thereof being incorporated herein byreference. All the references cited here are incorporated herein as awhole.

INDUSTRIAL APPLICABILITY

The glass substrate of the present invention is highly effective inreducing the dielectric loss of high-frequency signals and shows highthermal-shock resistance. Consequently, circuit boards employing theglass substrate are highly reduced in the transmission loss ofhigh-frequency signals and have excellent suitability for processingusing heat such as a laser.

Such glass substrate and circuit board are very useful as members forthe whole high-frequency electronic devices in which high-frequencysignals of higher than 10 GHz, especially signals of higher than 30 GHz,particularly signals of 35 GHz or higher are handled, as members forliquid-crystal antennas used in environments where temperaturefluctuations are large, or as members for devices or the like requiringperforation with a laser, etc.

REFERENCE SIGNS LIST

-   1 Circuit board-   2 Glass substrate-   2 a First main surface-   2 b Second main surface-   3 First wiring layer-   4 Second wiring layer

1. A glass substrate comprising, in mole percentage on an oxide basis:40% to 75% of SiO₂; 0.5% to 15% of Al₂O₃; 0.1% to 9% of MgO; 0% to 8% ofCaO; 0.1% to 13% SrO; and 0% to 10% of BaO, wherein the glass substratesatisfies the following relationship: {[Young's modulus (GPa)]×[averagecoefficient of thermal expansion at 50-350° C. (ppm/° C.)]}≤300(GPa·ppm/° C.), and has a relative permittivity as measured at 20° C.and 35 GHz of 10 or less and a dielectric loss tangent as measured at20° C. and 35 GHz of 0.006 or less.
 2. The glass substrate according toclaim 1, having the Young's modulus of 70 GPa or less.
 3. The glasssubstrate according to claim 1, having the average coefficient ofthermal expansion at 50-350° C. of 5 ppm/° C. or less.
 4. The glasssubstrate according to claim 1, having a relative permittivity asmeasured at 20° C. and 10 GHz of 10 or less and a dielectric losstangent as measured at 20° C. and 10 GHz of 0.006 or less.
 5. The glasssubstrate according to claim 1, having an area of a main surface of 100cm²-100,000 cm² and a thickness of 0.01 mm-2 mm.
 6. The glass substrateaccording to claim 1, wherein at least a part of an end surface thereofis chamfered.
 7. The glass substrate according to claim 1, having aVickers hardness of 400-550.
 8. The glass substrate according to claim1, having a cracking load of higher than 1.96 N.
 9. The glass substrateaccording to claim 1, having a density of 2.5 g/cm³ or less.
 10. Theglass substrate according to claim 1, having a compressive stress layerformed in at least a part of a surface of the main surface.
 11. Theglass substrate according to claim 1, having a porosity of 0.1% or less.12. The glass substrate according to claim 1, having a transmittance forlight having 350-nm wavelength of 50% or higher.
 13. The glass substrateaccording to claim 1, having a β-OH value of 0.05 mm⁻¹ to 0.8 mm⁻¹. 14.The glass substrate according to claim 1, comprising Al₂O₃ and B₂O₃ in atotal amount of 1-40%, having a content molar ratio represented by{Al₂O₃/(Al₂O₃+B₂O₃)} of 0-0.45, and comprising one or morealkaline-earth metal oxides in a total amount of 0.1-13%.
 15. The glasssubstrate according to claim 1, comprising one or more alkali metaloxides in a total amount of 0.001-5% in mole percentage on an oxidebasis.
 16. The glass substrate according to claim 15, having a contentmolar ratio represented by {Na₂O/(Na₂O+K₂O)} of 0.01-0.99, among thealkali metal oxides.
 17. The glass substrate according to claim 1,satisfying the following relationship of contents in mole percentage onan oxide basis:{1.02×SiO₂+3.42×Al₂O₃+0.74×B₂O₃+9.17×MgO+12.55×CaO+13.85×SrO+14.44×BaO+31.61×Na₂O+20.35×K₂O}≤300.18. The glass substrate according to claim 1, comprising A1₂0₃ in anamount of 0-10% and B₂O₃ in an amount of 9-30% in mole percentage on anoxide basis.
 19. The glass substrate according to claim 1, comprising Fein an amount of 0-0.012% in terms of Fe₂O₃ in mole percentage on anoxide basis.
 20. The glass substrate according to claim 1, which is foruse in a liquid-crystal antenna or a high-frequency circuit.
 21. Aliquid-crystal antenna comprising the glass substrate according toclaim
 1. 22. A high-frequency device comprising the glass substrateaccording to claim 1.